I think you are right with this. Current real capacity is about 54,700 max I believe. To get to 63,500 which is definitely the target requires 8,800 more. I can’t quite work out how the two tier option is 2,300 more than the south stand.
Edit - in fact I just have 160 in a row times and extra 15 rows is 2400 more seats. Surprising how a few extra rows makes such a difference. Basically the space where the boxes are is built over. Simple as that really.
Could we beat the 63,500 with safe standing?